Methods and systems for improved boundary contrast

Abstract

The present invention relates to methods and systems that define feature boundaries in a radiation sensitive medium on a workpiece using a diffraction-type micromirror array, extending to production of patterns and structures on a semiconductor substrate. Workpieces include lithographic masks, integrated circuits and other electronic and optical devices. Particular aspects of the present invention are described in the claims, specification and drawings.

1. A method of defining a feature boundary when exposing at least one radiation sensitive medium on a workpiece using a two-dimensional array of tilting micromirrors, the method including:
 tilting a first set of micromirrors on one side of the boundary to produce a high reflected output; 
 tilting a second set of micromirrors on an other side of the boundary past a tilt producing minimum reflected output intensity to a tilt producing substantially improved contrast along the boundary, as compared to the tilt producing minimum reflected output intensity. 
 
     
     
       2. The method of  claim 1 , wherein the tilt producing substantially improved contrast produces destructive interference between reflected output of the first and second sets of micromirrors. 
     
     
       3. The method of  claim 1 , further including tilting a third set of micromirrors, between the first and second sets of micromirrors, to an intermediate tilt. 
     
     
       4. The method of  claim 3 , wherein tilting the third set of mirror produces gray scaling corresponding to a monotonic function including a range from the tilt producing the high reflected output to the tilt producing the substantially improved contrast. 
     
     
       5. The method of  claim 1 , wherein the micromirrors tilt about a substantially central axis. 
     
     
       6. The method of  claim 1 , wherein the micromirrors tilt from one side. 
     
     
       7. The method of  claim 1 , wherein the tilting includes deforming supporting members of the micromirrors. 
     
     
       8. The method of  claim 1 , wherein the tilting includes deforming the micromirrors. 
     
     
       9. The method of  claim 1 , wherein the tilt producing substantially improved contrast corresponds to a substantially negative value of a real component of a complex amplitude of reflected output from the second set of micromirrors. 
     
     
       10. The method of  claim 1 , wherein the workpiece is a semiconductor substrate, further including:
 repeatedly tilting the micromirrors, illuminating the array with a partially coherent radiation and directing the reflected output to form at least one pattern in the radiation sensitive medium; and 
 processing the workpiece to form one or more semiconductor structures on the workpiece corresponding to the pattern. 
 
     
     
       11. The method of  claim 1 , wherein the workpiece is at least one reticle, further including:
 repeatedly tilting the micromirrors, illuminating the array with a partially coherent radiation and directing the reflected output onto the radiation sensitive medium; 
 developing a pattern on the reticle; and 
 form one or more semiconductor structures on a semiconductor substrate corresponding to the pattern. 
 
     
     
       12. A method of defining a feature boundary when exposing a radiation sensitive medium on a workpiece using a two-dimensional array of tilting micromirrors, the method including:
 tilting a first set of micromirrors on one side of the boundary to produce a high reflected output; 
 tilting a second set of micromirrors on an other side of the boundary, past a tilt producing maximum destructive interference within reflected output of the second set of micromirrors, to a tilt producing substantial destructive interference between the reflected outputs of the first and second sets of micromirrors. 
 
     
     
       13. A method of defining a feature boundary when exposing a radiation sensitive medium on a workpiece using a two-dimensional array of tilting micromirrors, the method including:
 tilting a first set of micromirrors on one side of the boundary to produce a high reflected output; 
 tilting a second set of micromirrors on an other side of the boundary past a tilt producing minimum reflected output intensity, to a tilt producing substantial destructive interference between the reflected output of the first and second sets of mirrors. 
 
     
     
       14. A controller for a two-dimensional array of tilting micromirrors defining a feature boundary when exposing a radiation sensitive medium on a workpiece, the controller including:
 logic and resources coupled to the array, adapted to drive a first set of micromirrors on one side of the boundary to tilt and produce a high reflected output, and 
 drive a second set of micromirrors on an other side of the boundary to a tilt, past a point of producing minimum reflected output intensity to a point of producing substantially improved contrast along the boundary, as compared to the tilt producing minimum reflected output intensity. 
 
     
     
       15. The tilting micromirror of  claim 14 , coupled to and controlled by the controller, including a reflecting surface footprint that has
 a substantially central tilting axis, 
 similar reflecting areas on opposing sides of the tilting axis, and 
 substantially less reflecting area away from the tilting axis than at or near the tilting axis. 
 
     
     
       16. The tilting micromirror of  claim 14 , coupled to and controlled by the controller, including a reflecting surface footprint that has
 a substantially central tilting axis, 
 similar reflecting areas on opposing sides of the tilting axis, and 
 substantially more reflecting area away from the tilting axis than at or near the tilting axis. 
 
     
     
       17. A pattern generator, including the controller of  claim 14 , further including:
 an illumination source, projecting radiation on the array; 
 optics, relaying the radiation reflected from the array to the radiation sensitive medium on the workpiece; and 
 a stage, supporting the workpiece, controlled to move as feature boundaries are defined. 
 
     
     
       18. The controller of  claim 14 , wherein the logic and resources are further adapted to drive a third set of micromirrors, between the first and second sets of micromirrors, to an intermediate tilt corresponding to a monotonic function, in a range including the tilt producing the high reflected output and the tilt producing the substantially improved contrast. 
     
     
       19. A pattern generator, including the controller of  claim 18 , further including:
 an illumination source, projecting radiation on the array; 
 optics, relaying the radiation reflected from the array to the radiation sensitive medium on the warkpiece; and 
 a stage, supporting the workpiece, controlled to move as feature boundaries are defined. 
 
     
     
       20. An article of manufacture including:
 a machine readable medium impressed with instructions to control defining a feature boundary when exposing a radiation sensitive medium on a workplace with a micromirror array, including instructions to 
 tilt a first set of micromirrors on one side of the boundary to produce a high reflected output; and 
 tilt a second set of micromirrors on an other side of the boundary past a tilt producing minimum reflected output intensity to a tilt producing substantially improved contrast along the boundary, as compared to the tilt producing minimum reflected output intensity. 
 
     
     
       21. A reflecting surface of a tilting micromirror adapted to be used in micromirror array, including:
 a reflecting surface footprint that has
 a substantially central tilting axis, 
 similar reflecting areas on opposing sides of the tilting axis, and 
 substantially less reflecting area away from the tilting axis than at or near the tilting axis; 
 
 wherein the reflecting surface has a range of tilts that includes
 a first tilt angle that produces a high reflected output and 
 a second tilt angle, beyond a tilt producing minimum reflected output intensity to a tilt producing substantially improved contrast, as compared to the tilt producing minimum reflected output intensity, between micromirrors assuming the first and second tilt angles. 
 
 
     
     
       22. A reflecting surface of a tilting micromirror adapted to be used in micromirror array, including:
 a reflecting surface footprint that has
 a substantially central tilting axis, 
 similar reflecting areas on opposing sides of the tilting axis, and 
 phase interference structures on opposing sides of the tilting axis, positioned such that the reflecting surface produces less reflected output intensity away from the tilting axis than at or near the tilting axis. 
 
 
     
     
       23. The reflecting surface of  claim 22 , wherein the reflecting surface footprint further includes opposing edges on opposite sides of the central tilting axis and the phase interference structures are positioned closer to the opposing edges than to the tilting axis. 
     
     
       24. The reflecting surface of  claim 22 , wherein reflecting surface footprint is adapted to arrangement so that centers of reflecting surfaces are aligned in rows and columns. 
     
     
       25. The reflecting surface of  claim 22 , wherein the phase interference structures differ in height from the reflecting surface itself by an odd multiple of a quarter wavelength.